PlayFab should make sure to stay on top of this new feature from Apple:
"Sign In with Apple will be available for beta testing this summer. It will be required as an option for users in apps that support third-party sign-in when it is commercially available later this year.
This means that, theoretically, anytime you see an option to sign-in to a service with Facebook or Google, you should also see an option to sign in with your Apple account. Thus, developers will be required to update their apps to integrate “Sign in with Apple.”"